Zn2+-Imidazole Coordination Crosslinks for Elastic Polymeric Binders in High-Capacity Silicon Electrodes.

Recent research has built a consensus that the binder plays a key role in the performance of high-capacity silicon anodes in lithium-ion batteries. These anodes necessitate the use of a binder to maintain the electrode integrity during the immense volume change of silicon during cycling. Here, Zn2+-imidazole coordination crosslinks that are formed to carboxymethyl cellulose backbones in situ during electrode fabrication are reported. The recoverable nature of Zn2+-imidazole coordination bonds and the flexibility of the poly(ethylene glycol) chains are jointly responsible for the high elasticity of the binder network. The high elasticity tightens interparticle contacts and sustains the electrode integrity, both of which are beneficial for long-term cyclability. These electrodes, with their commercial levels of areal capacities, exhibit superior cycle life in full-cells paired with LiNi0.8Co0.15Al0.05O2 cathodes. The present study underlines the importance of highly reversible metal ion-ligand coordination chemistries for binders intended for high capacity alloying-based electrodes.

Structural Analysis of Bottlebrush Block Copolymer Micelles Using Small-Angle X-ray Scattering.

We present structural analysis of spherical diblock copolymer micelles where core blocks have bottlebrush architecture. The dependence of the core radius (Rcore) and the corona thickness (Lcorona) on the core block length (Ncore) is investigated using small-angle X-ray scattering (SAXS) and discussed in terms of the stiffness of a core-forming polymer posed by its long fluoroalkyl side chains. The conformation of the core block is strongly stretched, and the measured exponents α and ß from power-law correlations, Rcore ∼ Ncoreα and Lcorona ∼ Ncoreß, respectively, are greater than those from any scaling predictions for block copolymer micelles with a flexible, linear core-block. Such deviations are attributed to the appreciable chain stiffness of the bottlebrush core block, and a simple model is suggested to understand how the core block stiffness influences both the dimensions of core and corona.

A Pyrene-Poly(acrylic acid)-Polyrotaxane Supramolecular Binder Network for High-Performance Silicon Negative Electrodes.

Although being incorporated in commercial lithium-ion batteries for a while, the weight portion of silicon monoxide (SiOx , x ≈ 1) is only less than 10 wt% due to the insufficient cycle life. Along this line, polymeric binders that can assist in maintaining the mechanical integrity and interfacial stability of SiOx electrodes are desired to realize higher contents of SiOx . Herein, a pyrene-poly(acrylic acid) (PAA)-polyrotaxane (PR) supramolecular network is reported as a polymeric binder for SiOx with 100 wt%. The noncovalent functionalization of a carbon coating layer on the SiOx is achieved by using a hydroxylated pyrene derivative via the π-π stacking interaction, which simultaneously enables hydrogen bonding interactions with the PR-PAA network through its hydroxyl moiety. Moreover, the PR's ring sliding while being crosslinked to PAA endows a high elasticity to the entire polymer network, effectively buffering the volume expansion of SiOx and largely mitigating the electrode swelling. Based on these extraordinary physicochemical properties of the pyrene-PAA-PR supramolecular binder, the robust cycling of SiOx electrodes is demonstrated at commercial levels of areal loading in both half-cell and full-cell configurations.

Highly Elastic Polyrotaxane Binders for Mechanically Stable Lithium Hosts in Lithium-Metal Batteries.

Despite their unparalleled theoretical capacity, lithium-metal anodes suffer from well-known indiscriminate dendrite growth and parasitic surface reactions. Conductive scaffolds with lithium uptake capacity are recently highlighted as promising lithium hosts, and carbon nanotubes (CNTs) are an ideal candidate for this purpose because of their capability of percolating a conductive network. However, CNT networks are prone to rupture easily due to a large tensile stress generated during lithium uptake-release cycles. Herein, CNT networks integrated with a polyrotaxane-incorporated poly(acrylic acid) (PRPAA) binder via supramolecular interactions are reported, in which the ring-sliding motion of the polyrotaxanes endows extraordinary stretchability and elasticity to the entire binder network. In comparison to a control sample with inelastic binder (i.e., poly(vinyl alcohol)), the CNT network with PRPAA binder can endure a large stress during repeated lithium uptake-release cycles, thereby enhancing the mechanical integrity of the corresponding electrode over battery cycling. As a result, the PRPAA-incorporated CNT network exhibits substantially improved cyclability in lithium-copper asymmetric cells and full cells paired with olivine-LiFePO4 , indicating that high elasticity enabled by mechanically interlocked molecules such as polyrotaxanes can be a useful concept in advancing lithium-metal batteries.

A one-pot synthesis of polysulfane-bearing block copolymer nanoparticles with tunable size and refractive index.

A one-pot synthesis of sulfur-rich polymer nanoparticles through a ring-opening metathesis polymerization is reported. The nanoparticles are formed in situ from diblock copolymers containing a polynorbornene derivative bearing cyclic polysulfanes. The refractive indices of the resulting nanoparticles are readily controlled in the range from 1.54 to nearly 1.65.